The flight control system of an aircraft forms the link between the control members (joystick, rudder bar, etc.) and the aerodynamic control surfaces (ailerons, vertical stabilisers, elevators, etc.). Modern airliners have electrical type flight control systems in which mechanical actions on the control members are converted into analogical signals which are transmitted to actuators manoeuvring the control surfaces.
A flight control system comprises in general a plurality of computers intended to receive information items from the control members and/or airplane sensors (accelerometer, gyrometer, inertial navigation system) and to determine from the information items received the flight controls to apply to the actuators.
Traditional flight control systems use specific computers for each flight control function and avionic buses of ARINC 429 or MIL-STD-1553 type, to transmit the commands to the actuators.
A more recent generation of flight control systems calls on Integrated Modular Architecture (IMA), in other words generic computers that come in practice in the form of electronic cards mounted in a rack of the avionics bay and which differ from each other essentially by the software that is executed therein. Furthermore, these new flight control systems use an AFDX (Avionics Full Duplex Switched Ethernet) communication network to transmit the controls to the actuators.
It will be recalled that the AFDX network, specifically developed for the needs of aeronautics, is based on a switched Ethernet network. A detailed description of the characteristics of this network may be found in the document entitled “AFDX protocol tutorial” available on the site www.condoreng.com as well as in the patent application FR-A-2832011 filed in the name of the applicant.
A description of a flight control system using an IMA architecture will moreover be found in the application FR-A-2943036 filed in the name of the present applicant.
FIG. 1 illustrates in a schematic manner the architecture of a flight control system, 100, known from the prior art. This system generally comprises a plurality of generic computers, 110, receiving information items coming from control members (not represented) as well as, if appropriate, from series of airplane sensors (also not represented). The computers determine from these information items the flight controls to apply to the actuators.
The computers transmit the control messages to the actuators via the AFDX network 120. More precisely, each actuator is equipped with a terminal 130, subscribed to the AFDX network, capable of receiving the control messages and sending back information or acquittal messages to the computers. An actuator may moreover be equipped with sensors making it possible to measure the position of the actuated control surface, in which case the associated terminal can also send back to the computer that controls it the information items of the position measure in question. Hereafter, for reasons of commodity, reference will be made indiscriminately to the actuator or to its associated terminal, 130, it being understood that an actuator subscribed to the network is in fact an actuator equipped with a terminal subscribed to the AFDX network.
The AFDX network comprises a plurality of frame switches 140 installed in the avionics bay (demarcated in the figure by a broken line) and switching the virtual links going to and/or coming from different subscribers to the network, in particular the virtual links connecting the computers 110 and the subscribed actuators 130.
In order to reduce the number and the length of the wired links, the AFDX network may comprise frame switching equipment designated micro-switches. These micro-switches make it possible to treat locally the frames coming from or going to a cluster of terminals subscribed to the network. More precisely, a micro-switch has a first port, generally connected to an AFDX switch or directly to a computer, and a plurality of second ports connected to the different subscribed terminals. On the downlink, in other words for frames received by the first port going to a subscribed terminal, the micro-switch plays the role of repeater (hub), in other words that an incident frame on the first port is replicated on all the second ports. The subscribed terminals that receive it determine whether they are addressees, and ignore it in the negative and take it into consideration in the affirmative. On the other hand, on the uplink, in other words for frames transmitted by the different subscribed terminals, the micro-switch scans in turn the second ports and empties their respective buffers on the first port, according to a “round robin” type mechanism, thereby assuring an equitable sharing of the pass band.
It will be noted that the flight control system illustrated in FIG. 1 comprises a plurality of such AFDX micro-switches, 150, each connected to a switch of the avionics bay. A virtual link connecting a computer and an actuator passes via one or more switches, then, if needs be via a micro-switch.
Each computer 110 comprises two calculation modules, namely a control module, 111, known as COM module, and a surveillance module, 112, known as MON module. The MON and COM modules are of identical structure and only differ by the manner in which they are programmed (different algorithms). A COM module may be reconfigured into a MON module and vice versa. The MON and COM modules come in practice in the form of IMA cards mounted in a rack or IMA box of the avionics bay.
The COM module transmits to the actuators control messages via the AFDX network and receives information or confirmation messages from the latter.
The MON module also receives the information or confirmation messages from the actuators and verifies the coherence between the control messages sent by the COM module and the information or confirmation messages that are returned to the latter by the different actuators. The MON module may thus detect a failure of the actuator controlled by the MON module.
In a symmetrical manner, each terminal 130 associated with an actuator is generally equipped with a control module, COM, represented by 131 and a surveillance module, MON, represented by 132. The COM module is charged with applying the electrical orders as a function of the control messages transmitted by the computer. The MON module is for its part charged with verifying whether the electrical orders transmitted by the COM module to the actuator are indeed coherent with the commands transmitted by the computer and, in the event of an anomaly, to notify thereupon the computer.
The COM module of a computer is connected to the COM modules of the actuators that it controls. COM A link commonly designates the link between a COM module of a computer and a COM module of an actuator. In a dual manner, the MON modules of these actuators are connected to the MON module of the computer in question. In a similar manner, MON link designates a link between a MON module of a computer and a MON module of an actuator.
In current flight control systems, the COM and MON links are spatially segregated. In other words, the COM links and the MON links do not share any common element of the AFDX network. They do not use in particular the same switches or micro-switches and do not use the same wired links. The aim of this spatial segregation is to avoid a simultaneous corruption of the information items on the two links and thus to maintain a high level of reliability.
Finally, the AFDX network is made redundant to satisfy the requirements of availability. In other words, the subscribers of the network are connected to two identical AFDX networks (also known as network layers), designated by A and B. Thus, each COM module of a computer comprises a first port, PCCOMA, connected to the layer A and a second port PCCOMB connected to the layer B. The COM module of the recipient terminal also comprises a port PECOMA connected to the layer A and a port PECOMB connected to the layer B. When the COM module of a computer transmits a control message to the recipient terminal, two identical messages are in fact transmitted in parallel by the ports PCCOMA and PCCOMB, respectively on the layers A and B. A COM A link and a COM B link are then distinguished according to the network through which the COM link transits.
In the same way, each MON module of a computer or of a recipient terminal comprises a first port, PCMONA connected to the network A and a second port, PCMONB, connected to the network B. A MON A link and a MON B link are then distinguished, according to the network through which the MON link transits. In all cases, the messages transmitted on the two networks A and B are strictly identical.
The spatial segregation constraints on the one hand and the redundancy of the AFDX network on the other hand imply that, for each computer 110 controlling an actuator 130, four cables are necessary, corresponding respectively to the COM A, COM B, MON A, MON B links. Given that most control surfaces are situated far from the avionics bay, the amount of cabling necessary to connect the actuators to the nodes of the network is thus particularly important.
The aim of the present invention is consequently to propose an aircraft control system overcoming the aforementioned drawbacks, in particular to reduce the cabling between the avionics bay and the actuators without sacrificing the aforementioned reliability and/or availability requirements.